Why RGB values on transparent pixels is (71,112,76)

[shanegxxiao]

After compare several pairs images processed by pngquant, it seems pixel with rgba = (0, 0, 0, 0) was modified to (71, 112, 76, 0), How is it happen? It makes premultiply alpha works failed.

[kornelski]

No, it's not a failure. When alpha=0 these values have no meaning. They're visible only in software that incorrectly drops the alpha channel, and in that case they're useful for diagnosing the error.

[shanegxxiao]

Thanks first, and sorry for the late reply. Is it possiable to keep the original RGB values event alpha is zero in the images processed by pngquant?

[kornelski]

I've intentionally made it completely impossible. Indexed 8 bit color can't afford it, so RGB of transparent colors is the first thing pngquant completely clears.